@kengtekeng No clue, I only read the chapters released here on mangadex.
I just assume he gets a harem cause of the first 7 (way too short and abruptly ending) chapters of the manga (aka the story so far up until this chapter). He had a girl profess her love for him when he was kicked out (although she stupidly enough never actually said it), he had a yuri pair be kind to him, he found a half-naked girl attacked by a monster, and its a "got called useless, was actualyl op" isekai story. But if you say there is no harem tag, then maybe I am wrong? I never checked the tags.